Update help text for [ml2] path_mtu

[Ihar Hrachyshka]

This help message is not optimal and overloaded with details. While at it, physnet_mtus option refers to segment_mtu that does not even exist anymore since Mitaka.

[OpenStack Infra (hudson-openstack)]

Related fix proposed to branch: master
Review: https://review.openstack.org/302089

[Ihar Hrachyshka (ihar-hrachyshka)]

There are use cases to set path_mtu different from global_physnet_mtu (even if not common).

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/302089
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=403e5a07f51dee1efd335011cdd6b4454d1e7fde
Submitter: Jenkins
Branch: master

commit 403e5a07f51dee1efd335011cdd6b4454d1e7fde
Author: Ihar Hrachyshka <email address hidden>
Date: Wed Apr 6 10:05:13 2016 +0200

    Fixed help messages for path_mtu and global_physnet_mtus options

    For path_mtu, make it clear it applies to tunnel typed tenant networks.
    Removed information about specific mechanisms used to advertise MTU
    values to instances because a) it duplicates the global_physnet_mtu
    option description; b) it is not complete now that we also advertise MTU
    via RAs. Finally, removed description for calculation details because
    they duplicate global_physnet_mtu description.

    While at it, fixed help text for global_physnet_mtus option not to refer
    to segment_mtu which was renamed into global_physnet_mtu lately.

    Change-Id: Ib0010206f08ec9a76b0e26e84cdb03c80755908d
    Related-Bug: #1566706

[OpenStack Infra (hudson-openstack)]

Related fix proposed to branch: stable/mitaka
Review: https://review.openstack.org/322787

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/322787
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=bd8adf3ee004d8155686ec05c18b31c3b9359c80
Submitter: Jenkins
Branch: stable/mitaka

commit bd8adf3ee004d8155686ec05c18b31c3b9359c80
Author: Ihar Hrachyshka <email address hidden>
Date: Wed Apr 6 10:05:13 2016 +0200

    Fixed help messages for path_mtu and global_physnet_mtus options

    For path_mtu, make it clear it applies to tunnel typed tenant networks.
    Removed information about specific mechanisms used to advertise MTU
    values to instances because a) it duplicates the global_physnet_mtu
    option description; b) it is not complete now that we also advertise MTU
    via RAs. Finally, removed description for calculation details because
    they duplicate global_physnet_mtu description.

    While at it, fixed help text for global_physnet_mtus option not to refer
    to segment_mtu which was renamed into global_physnet_mtu lately.

    The cherry-pick differs from the master patch, as Mitaka still uses
    a default value of 1500 for path_mtu. Master uses 0. The effect is,
    that with Mitaka you have to override the default 1500 path_mtu
    value to use jumbo frames, while with master the default 0 value is
    being ignored. There it's sufficient to specify the global_physnet_mtu
    only.

    Change-Id: Ib0010206f08ec9a76b0e26e84cdb03c80755908d
    Related-Bug: #1566706
    (cherry picked from commit 403e5a07f51dee1efd335011cdd6b4454d1e7fde)

[OpenStack Infra (hudson-openstack)]

Related fix proposed to branch: stable/mitaka
Review: https://review.openstack.org/329782

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/329782
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=f9d5064c22f07ca5df94deb9f2c1f5dfb2c6ba66
Submitter: Jenkins
Branch: stable/mitaka

commit f9d5064c22f07ca5df94deb9f2c1f5dfb2c6ba66
Author: Andreas Scheuring <email address hidden>
Date: Wed Jun 15 09:08:30 2016 +0200

    Fixed help messages for path_mtu and global_physnet_mtus options

    Giving better recommendations for meaningful values.

    Change-Id: Iea4a343465f06ba19fc8e504fc0ca329a718a8c5
    Related-Bug: #1566706